One of the major problems that telecommunications operating companies faced with is the need to install infrastructures to give service in certain areas of low subscriber density where the economic return is very poor as a result of the widespread geographical distribution of the customers.
This is particularly the case in the access part of the network in environments with a certain demand where, in addition, the installation and provision of these services have to be implemented rapidly.
To resolve these problems, in recent years use has been made of what is normally termed radio access, in which a set of base stations of wireless communications systems (cellular, point to multipoint, etc.) provide radio coverage for a certain zone in which are installed a number of "special" wireless terminals, which are cordless terminals of the type normally used in such communications systems but into which a line interface circuit has been incorporated, while personal interfaces (microphone, loudspeaker, keypad, display element) have been suppressed. This line interface performs the functions of conversion required for both directions of transmission, so that, from a conventional telephone set connected to this terminal, it is possible to offer the same kind of functions as with a fixed telephone connected directly to the public switched network.
Among these functions are to be found those of four-to-two wire conversion, user signal tone generation, dial signal conversion, etc.
In this way it is possible to have a set of fixed telephones that have access to the public switched network by means of a wireless communications network. There is no mobility provided by this communications network, so that a new wireless communications system would be necessary with the consequent duplication of equipment and the possible saturation of the radiofrequency spectrum, should the subscribers also wish to have cordless telephones to provide a desired mobility within an area similar to that covered by the wireless network.